Method for spinning polyamide yarn of increased relative viscosity



United States Patent O 3,551,548 METHOD FOR SPINNING POLYAMIDE YARN OFINCREASED RELATIVE VISCOSITY Edmond P. Brignac, 782 Whitney Drive 32503;Bascum H. Duke, 1118 Dunmire St. 35204; and Walter J. Nunning, 2375Scenic Highway, Apt. 210 32503, all of Pensacola, Fla.; and Rupert J.Snooks, Jr., 402 Poinciana Drive, Gulf Breeze, Fla. 32561 No Drawing.Filed Jan. 8, 1968, Ser. No. 696,108 Int. Cl. B28b 3/20; B29c 25/00 US.Cl. 264234 5 Claims ABSTRACT OF THE DISCLOSURE Continuous-filament highrelative viscosity polyamide yarn is provided by fabricatingcontinuous-filament yarn from polyamide containing from 0.01 to byweight of certain phosphorous compounds, drawing the yarn andsubsequently heating the drawn yarn below its melting point.

BACKGROUND OF THE INVENTION The present invention relates to a processfor spinning continuous-filament polyamide yarn having a high relativeviscosity and desirable properties.

As used herein the expression relative viscosity refers to the ratio ofabsolute viscosity in centipoises at 25 C. of a 10% solution of polymerin solvent to the absolute viscosity also in centipoises at 25 C. of thesolvent; solvents generally used for this purpose include: aqueous 90%formic acid, aqueous 85% phenol and meta-cresol. Relative viscosity (Nof a polymer may be used to determine the intrinsic viscosity [N]thereof from which the molecular weight of the polymer can be determinedaccording to the equation:

where M represents molecular weight, and K and a are constants anddepend on the properties of solvent and polymer molecules and on theirinteraction. Therefore, relative viscosity values are an indication ofpolymer chain length and increase as the molecular weight of the polymerincreases. Unless otherwise specified relative viscosity values aredetermined using aqueous 90% formic acid as the solvent according to theabove procedure.

Continuous-filament high relative viscosity polyamide yarn is desirable,especially in applications Where yarn properties such as tenacity andstrength are important, for example in tire yarn. Present melt-spinningtechnology, however, permits fabrication of continuous-filament yarnfrom polyamide having a relative viscosity of less than about 90. Higherrelative viscosity polyamides have high melt-viscosities which createnumerous processing and handling problems in the fabrication andprocessing of filaments, e.g. in pumping and spinning of the moltenpolymer and in subsequent drawing of the filaments. More specifically,during melt-spinning operations high relative viscosity polyamide tendsto resist filtration through conventional sand packs as well asextrusion through spinneret capillaries which eventually results incessation of operations. Therefore, continuous-filament nylon 66 yarn,for example, has heretofore been limited to yarn having relativeviscosities ranging up to about 90. Nevertheless industry recognizesthat in certain applications higher relative viscosity polyamide yarnwould be desirable, since the physical properties of polyamides tend toimprove with increases in the molecular weight thereof.

SUMMARY OF THE INVENTION Continuous-filament high relative viscositypolyamide yarn is provided by the process of the present invention whichcomprises: fabricating continuous-filament polyamide yarn from polyamidecontaining from 0.01 to 15% by weight of a phosphorous compound; drawingthe yarn up to about six times its length; arranging the drawn yarn in aheating vessel such that all surfaces of the yarn are permeable togaseous substances; heating the drawn yarn in the vessel under vacuum orin an inert gas sweep to effect solid-state polymerization of thepolyamide; removing the resulting yarn from the vessel and, if desired,hot-stretching the yarn to at least 15 of its drawn length.

Solid-state polymerization has been used in the past to increase therelative viscosity or molceular Weight of polymer pieces, e.g. chips,flake, pellets, articles, and the like. Three chemical reactions havebeen observed in solid-state polymerization reactions, which are: (1)condensation resulting in increased relative viscosity and molecularweight of polymer chain, and competing surface reactions involving (2)oxidation and (3) hydrolysis which cause embrittlement of polymerleading to chain scissions and molecular weight reductions. In the caseof polymer pieces, reactions (2) and (3), which occur at the surfacethereof, are overshadowed by reaction (1) due to the small surface tovolume ratios of polymer pieces. On the other hand, polymer filamentshave large surface to volume ratios and normally exposure to solidstatepolymerization conditions would be expected to actually result in adecrease in yarn relative viscosity. The unexpected increase in relativeviscosity attained by the process of the present invention is believedto result from the presence of the phosphorous compound in the yarn.

Fiber-forming polyamides which may be used to fabricate the yarn of thepresent invention are synthetic linear polycarbonamides characterized bythe presence of recurring carbonamide groups as an integral part of thepoly mer chain which are separated from one another by at. least twocarbon atoms. Polyamides of this type include polymers, generally knownin the art as nylons, obtained from diamines and dibasic acids havingthe recurring unit represented by the general formula:

NHCORCONHR in which R is an alkylene group of at least two carbon atoms,preferably from 2 to 10; and R is selected from R and phenyl groups.Also, included are copolyamides and terpolyamides obtained by knownmethods, for example, by condensation of hexamethylene diamine and amixture of dibasic acids consisting of terephthalic acid and adipicacid. In addition to the above polyamides, the polyamides also includepolyamides obtained from amino acids and derivatives thereof.

Polyamides of the above description are well-known in the art andinclude, for example, the copolyamide of 30% hexamethylene diammoniumisophthalate and hexamethylene diammonium adipate, polyhexamethyleneadipamide .(nylon 66), polycaprolactam (nylon 6), polyhexamethylenesebacamide, and polyhexamethylene adipamide-containing polymers, such aspolymers containing polyhexamethylene adipamide and polyhexamethyleneisophthalamide, or polyhexamethylene terephthalamide or polycaproamide,or combinations thereof.

To attain high relative viscosity polyamide yarn via the process of thepresent invention the polyamide must contain 0.01 to 15% by Weight of atleast one phosphorous compound selected from compounds represented bythe formulas:

wherein R is a C to C hydrocarbon radical selected from alkyl,cycloalkyl, aryl or arylalkyl groups; X is hydrogen or R; Y is X, anammonium cation, or

cation; where m is an integer from 2 to 10; and n is an integercorresponding to the valance of the metal. Generally, the alkyl groupshave from 1 to 5 carbons and the cycloalkyl groups from 5 to carbonatoms. Suitable metals include sodium, potassium, lithium, calcium,cesium, tin, rubidium, and the like, i.e. metals listed in Groups IIV ofthe Periodic Table of Elements. Exemplary phosphorus compounds which maybe used in carrying out the present invention include phenylphosphinicacid, diphenylphosphinic acid, sodium phenylphosphinate,dimethylphosphinic acid, phenylphosphonic acid, triphenylphosphite,ethylphosphonic acid, ethylphenylphosphonic acid, alkylene diammoniumarylphosphinates, such as hexamethylene diammonium phenphosphinate, andthe like. The phosphorus compound may be incorporated into a polyamideby adding the compound to the monomeric polyamide-forming materialsbefore polycondensation or by adding it to and mixing it with moltenpolyamide.

The manner in which the yarn is fabricated from polyamide materialscontaining the above-specified phosphorous compounds and subsequentlydrawn are not critical to the invention and may be done according toconventional techniques. Thus, yarn may be fabricated by melt-spinning,i.e. extruding molten polyamide containing said phosphorous compoundthrough capillaries of a spinneret into molten streams of polyamidewhich are solidified into filaments. The filaments are gathered andsubsequently drawn by stretching them about 400%.

The drawn yarn, when heated in the heating vessel to effect solid-statepolymerization, must be arranged so that gaseous by-products formed as aresult of oxidation and hydrolysis surface reactions can diffusetherefrom. These by-products, if trapped within the yarn, offset theeffects of the polycondensation reaction and result in an overalldecrease in yarn relative viscosity. Yarn arrangements which aresatisfactory for use in the process of the present invention arearrangements wherein interstices exist between adjacent yarn strandsduring processing whereby by-products can permeate the yarn.

However, in conventional drawing operations, after the yarn is drawn andWound onto bobbins, it partially retracts or recovers from the drawingimparting tension and compressive forces to the yarn. With this yarnarrangement, referred to as high tension bobbins, no interstices existbetween yarn strands and as a result gaseous by-products cannot permeatethe inner yarn, i.e. portions of the yarn would not be exposed to anatmosphere suitable for solid-state polymerization. Therefore, yarnwound onto bobbins in this manner must be rearranged before it issuitable for use in the present invention.

Conveniently, yarn may be unwound from high tension bobbins and woundonto bobbins in a crisscross fashion whereby a plurality of congruent,evenly spaced, diamond-shaped patterns are formed; the center of thediamond is void of yarn and is defined by the yarn windings.

The diamond size may be varied, as desired. The tension applied to theyarn in winding it onto bobbins to form the diamond pattern is,preferably, only sufiicient to maintain the yarn on the bobbins. Otherarrangements of yarn suitable for use in the invention are: strands,skeins, hanks, or any arrangement which permits gaseous byproducts topermeate the yarn during the heating thereof.

The yarn, arranged as described above, may be heated in any suitablevessel, such as a vacuum oven or vented oven, which may be heated by anysuitable means, e.g. electricity, gas, steam, etc. During heating,by-products are formed which should be removed from yarn surfaces and,preferably, from the vessel. Removal of the byproducts may beaccomplished by means of vacuum or inert gas sweep, e.g. a nitrogensweep. The ultimate relative viscosity attained by the process of theinvention is a function of oven time and temperature. Oven temperaturesmay range from C. to 5-l0 C. below the melting point of the polyamide.Oven times may vary from one hour or less to several days or moredepending on relative viscosity desired and also on oven temperaturesemployed. Generally, oven times of 1 to 24 hours are adequate.

The yarn in addition to the phosphorous compound may contain otheradditives which are commonly incorporated into monomeric mixes prior topolycondensation or the fabricated yarn may be coated with additiveswhich are applied as a finish. Thus, monomeric mixes may contain smallamounts 0.01 to 10% on weight of monomer, for example, of acetic acid(viscosity stabilizer); copper acetate and potassium iodide (heatstabilizers); p,p-dioctyldiphenylamine, other amines, or manganoushypophosphite and/or hindered phenols (oxidation stalizers); titaniumdioxide (delustrant); etc., oils, waxes and the like or any combinationof these. Since in processing yarn according the present invention theyarn is heated for substantial periods of time, heat stabilizers arepreferably incorporated into the yarn, although the presence of thesestabilizers have no influence on RV.

DESCRIPTION OF THE PREFERRED EMBODIMENT The following examples are givenfor purposes of iilustrating the invention. However, the scope of theinvention is not intended to be limited to the particular compounds,ranges or conditions recited therein.

Examples 1 and 2 illustrate the affect oven time and temperature duringprocessing have on the ultimate relative viscosity of the yarn. Example3 shows that the process of the present invention results in solid-statepolymerization, rather than cross-linking. Example 4 demonstrates thatimproved yarn properties are obtained by processing yarn according tothe invention process. Example 5 shows that tenacity losses resultingfrom processing yarn according to the invention may be regained and evenimproved by hot-stretching the processed yarn.

In the examples RV; refers to relative viscosity determined usingaqueous 90% formic acid and RV refers to relative viscosity determinedusing aqueous 85% phenol.

EXAMPLE 1 Hexamethylene diammonium adipate (nylon salt) and a mixture of70% nylon salt and 30% hexamethylene diammonium terephthalate, eachcontaining 88 p.p.m. copper as copper acetate, 510 p.p.m. potassium aspotassium iodide and 154 p.p.m. phenylphosphonic acid, were eachpolymerized, spun and drawn into 70 RV;84O denierl40 filament yarn(designated as Yarn A) and 20 RV 840 denier filament yarn (designated asYarn B), respectively. The drawn yarns were unwound from standarddrawtwist bobbins and wound in a crisscross fashion onto bobbins withlow tension being applied to the yarn. Bobbins of each yarn were placedin a vacuum oven and processed 15 hours at specified temperaturesranging from 140 to 220 C. and 30 inches Hg vacuum. The RV and RV,, ofthe yarn on each bobbin was determined; no gel was observed when theyarn was dissolved in its respective solvent, indicating thatcross-linking had not occurred. The results are given in Table I.

Yarn A arranged on bobbins in a crisscross fashion as described inExample 1 were processed in a vacuum oven at 195 C. and 30 inches Hgvacuum for specified periods of time ranging from 5 hours to 20 hours.The RV of the yarn was determined after various time periods. Noevidence of cross-linking was observed. The yarn RVs are given in TableII.

TABLE II Hours: Yarn A, RV; 5 118 138 The data in Tables I and II showthat relative viscosity increases with increases in oven temperature andtime.

EXAMPLE 3 To demonstrate that the process of the invention results in anincrease in relative viscosity via solid-state polymerization of thepolyamide with substantially no crosslinking, the following experimentwas conducted: Three samples having the composition of Yarn B werefabricated, drawn and treated in an electric oven at 160 C. with anitrogen purge (100 cc. per minute). Each sample was placed into analuminum cup. Before treatment and at the end of 4 hours of treatmentthe RV and available end groups (NH and COOH) were determined. The endgroup analysis was carried out by dissolving 2 gram samples of the yarnin aqueous 85% phenol and titrating with 0.1 N HCl to find theinflection point; a second yarn sample was prepared in the same mannerand titrated this time with 0.1 N NaOH to find the inflection point; thesolvent per se is also titrated with each agent to find the respectiveinflection points. Then the inflection point of the solvent whentitrated with 0.1 N HCl is subtracted from the inflection point ofsolvent plus sample when titrated with 0.1 N HCl to find mil-equivalentsper gram of NH end group. The same procedure is repeated only with theinflection points determined when titrating with 0.1 N NaOH to findmil-equivalents per gram of COOH end group. The results are tabulated inTable III.

The data show that an increase in yarn relative viscosity is accompaniedby a decrease in reactive and groups, indicating polymerization.Moreover, no gel was observed when the samples were placed in solventwhich is further indicative that no cross-linking occurred.

6 EXAMPLE 4 Yarn B was processed in a vacuum oven at 30 inches Hg vacuumfor 16 hours at C. (Run 1) and at C. (Run 2); and the RV dry retraction,boil shrinkage and impact strength of the processed yarn were determinedand compared with Yarn B not processed according to the presentinvention and designated as control yarn in Table IV.

TABLE IV Dry Boil-01f Impact retraction, shrinkage, strength, Yarn B RVpercent percent grams/denier Control l9 2. 6 l0. 8 9. 4 Run 1 28 0. 010.3 12. 3 Run 2 36 0. 03 O. 0 11. 4

The data of Table IV show that the impact strength, and particularly theboil-off shrinkage, and dry retraction properties of nylon yarn areenhanced by the process of the invention.

EXAMPLE 5 Processing yarn according to the procedure of Example 1results in a slight decrease in the tenacity of the yarn. However, thisloss can be regained and the tenacity even increased beyond that ofunprocessed yarn by hot-stretching the yarn at least 15% of its length,according to conventional techniques. To demonstrate this effect, YarnB, designated in Table V as Yarn B having a RV of 27, after beingprocessed according to the invention in a vacuum oven at 30 inches Hgfor 15 hours at C. was hot-stretched 15 and 25%. For purposes ofcomparison the tenacity of Yarn B (not processed) having a RV of 20 wasalso determined. Additionally, the tenacity of unprocessed Yarn Bhot-stretched 14% (corresponding to conventional hot-stretched tireyarn) is also given.

TABLE V Oven process- Hot-st etching, Tenacity, gms./

Yarn B, RV ing, C percent den.

None None 6. 3

None 14 6. 6

195 None 6. 2

From the foregoing examples, it is apparent that the relative viscosityof polyamide yarn can be increased and the properties thereof enhanced,particularly the boil-off shrinkage characteristics thereof, by theprocess of the present.

Thus far the invention has been used primarily to increase the relativeviscosity and enhance the properties of continuous-filament yarnfabricated from nylon 66 and nylon-containing polymers, e.g. thecopolymer formed from hexamethylene diammonium adipate and hexamethylenediammonium terephthalate. However, the process can effectively becarried out with any continuous-filament polyamide yarn so long as theyarn contains from 0.01 to 15% p.p.m. of at least a one-phosphoruscompound of the type described herein.

What is claimed is:

1. A process of increasing the relative viscosity of con-'tinuous-filament, drawn polyamide yarn which comprises:

(a) fabricating said yarn from a polyamid containing from 0.01 to 15% byweight of yarn of at least one phosphorous compound selected from thegroup conwherein R is a C to C alkyl group, a C to C cycloalkyl group,phenyl group or an alkyl-substituted 7 phenyl group having from 6 to 10carbon atoms; X is R or hydrogen; Y is X, an ammonium cation or cationWhere m is an integer from 2 to 10; and n is an integer corresponding tothe valence of the metal, said metal being a Group I to IV metal of thePeriodical Table;

(b) arranging said polyamide yarn in a heating vessel such that allsurfaces thereof are permeable to gaseous substances;

(c) heating said arranged polyamide yarn at temperatures ranging fromabout 125 C. to about C. below the melting range thereof; and

(d) removing from said vessel gaseous substance formed during heating ofsaid arranged polyamide yarn.

2. The process as defined in claim 1 wherein the phosphorous compound isphenylphosphinic acid.

3. The process as defined in claim 1 wherein the polyamide ispolyhexamethylene adipamide.

4. The process as defined in claim 1 wherein the poly- 2d amide is acopolymer of (1) hexamethylene diammonium adipate and (2) hexamethylenediammonium terephthalate.

5. The process of claim 4 wherein the copolymer consists of (1) and 30%(2).

References Cited UNITED STATES PATENTS 2,927,841 3/1960 Ben 294-211X2,996,466 8/1961 Kessler 264-211X 3,040,005 6/1962 Bernhardt et al.260-78 3,078,248 2/1963 Ben 264-211 3,150,435 9/1964 McColm et a1.264-346X 3,161,710 12/1964 Turner 260-MX 3,340,339 9/1967 Ullman264-168X 3,378,532 4/1968 Fritz et a1 260-78 SC 3,404,140 10/1968Fukumoto 260-93.7

FOREIGN PATENTS 1,004,558 9/1965 Great Britain 260-78 JULIUS FROME,Primary Examiner J. H. WOO, Assistant Examiner US. Cl. X.R.

